1. Field of the Invention
The present invention relates to a fluid-filled vibration damping device which has a pressure-receiving chamber filled with a non-compressible fluid whose pressure changes upon application of a vibrational load thereto, and whose vibration damping characteristic can be suitably adjusted by controlling the pressure of the fluid within the pressure-receiving chamber.
2. Discussion of the Related Art
As one kind of a vibration damper interposed between two members of a vibration system so as to connect these two members in a vibration damping manner or mount one of these members on the other member in a vibration damping manner, there is known a fluid-filled vibration damping device having an elastic body which elastically connects a first and a second mounting member that are disposed in mutually spaced-apart relationship with each other. The elastic body partially define a pressure-receiving chamber filled with a non-compressible fluid the pressure of which changes upon application of a vibrational load between the first and second mounting members. JP-A-60-8540 and JP-A-61-2939 show examples of such a fluid-filled vibration damping device, wherein the pressure-receiving chamber is partially defined by a movable member which is movable or displaceable relative to the first and second mounting members. The vibration damping characteristic of this type of vibration damping device can be adjusted as desired by oscillating the movable member at a frequency corresponding to the frequency of the vibrations to be damped, so as to control the fluid pressure within the pressure-receiving chamber. Thus, the fluid-filled vibration damping device of the type described above exhibits a controlled vibration damping characteristic suitable for effectively damping the input vibrational load.
The known fluid-filled vibration damping device described above must have electromagnetic drive means for oscillating the movable member, as described in the above-identified publications. The electromagnetic drive means includes a relatively large number of comparatively expensive components such as a permanent magnet and a coil. Accordingly, the damping device is difficult to manufacture at a low cost, and inevitably has relatively large size and weight.
For assuring a sufficient degree of stability of the electromagnetic force generated by the electromagnetic drive means, the permanent magnet, coil and other components must be built in the damping device with high positional and dimensional accuracy, requiring a highly sophisticated technique for the manufacture of the damping device, thereby reducing the efficiency of large-scale production.
The known fluid-filled vibration damping device suffers from other drawbacks such as a temperature rise due to heat generated by energization of the coil, and a relatively large amount of electric power consumption, where the fluid pressure in the pressure-receiving chamber is kept controlled for a long time or controlled with a considerably large force of oscillation of the movable member.